The present invention relates to a temperature stable dielectric and, in particular, to a barium titanate dielectric composition which remains stable at high temperatures, which can be used to produce multilayer ceramic capacitors with base metals, such as nickel as internal conductive electrodes. The multilayer capacitors thus produced have a variation of capacitance with temperature of less than .+-.20% over the temperature range -55.degree. C. to 140.degree. C. as compared to the value at 25.degree. C. and no second phases were apparent in the microstructures.
The present invention also relates to a temperature stable dielectric and, in particular, to a barium titanate dielectric composition, which can be used to produce multilayer ceramic capacitors with noble metals, such as palladium or palladium/silver alloys, as internal conductive electrodes. The multilayer ceramic capacitors thus produced have their variation of capacitance with temperature less than .+-.20% over the temperature range -55.degree. C. to 140.degree. C. as compared to the value at 25.degree. C. In a further embodiment of the invention the variation of capacitance with temperature is less than .+-.15% over the temperature range -55.degree. C. to 145.degree. C. as compared to the value at 25.degree. C. The ceramic microstructures of the above capacitors do not contain second phases when examined by Scanning Electron Microscopy using electron backscattering.
Multilayer ceramic capacitors are well known in the art and have been manufactured for many years by a variety of processes, all of which result in alternate layers of a ceramic dielectric composition and metal in the devices. The typical manufacturing processes require the co-sintering of the ceramic dielectric composition and metal to consolidate these materials into working devices. The co-sintering process is generally carried out in an air atmosphere and thus the inner electrodes of the devices generally comprise a precious metal such as platinum, gold, palladium, or alloys thereof, to avoid oxidation during the sintering process.
Inner electrodes made from precious metals are very expensive. Ceramic dielectric materials for the manufacture of temperature stable multilayer ceramic capacitors with nickel inner electrodes have been reported in the articles and patents described below. In all of these cases a variation of capacitance with temperature of less than .+-.15% over the range -55.degree. C. to 125.degree. C. as compared to the value at 25.degree. C. is exhibited.